This invention relates to a rotation-braking damper for braking and absorbing opening and closing motions of an opening-closing object such as a lid or a door.
For the purpose of absorbing a rising motion which the cassette tape holder in a cassette recorder or video tape recorder produces after it has been released from its contained state, the friction type damper (Japanese Utility Model Application Disclosure SHO No. 55(1980)-75805) and the oil type damper (U.S. Pat. No. 4,342,135) have been adopted. The friction type damper is defective in that it does not produce smooth braking, gives an uncomfortable sensation upon the user's hand, and is complicated in structure. The oil type damper entails problems of its own which, unlike the problems suffered by the friction type damper, are ascribable to the use of oil. To be specific, this damper uses a silicone oil of high viscous drag. This silicone oil has an unusually high thermal expansion coefficient and, therefore, is readily expanded by a rise in the temperature of the ambient air. When the temperature of the ambient air of the recorder using the oil type damper rises, therefore, the oil is inflated and consequently leaks through the gap between the case forming a housing for the cassette and the cap or the gap between the shaft of a toothed wheel and the hole in the case penetrated by the shaft and soils the exterior of the case. When the temperature falls, the oil within the housing shrinks and this decrease in the volume of the oil deprives the damper proportionately of its effect. To avoid the trouble, the housing is required to incorporate therein a device adapted to absorb the voluminal change of the oil. The use of this device entails an addition to the number of component parts of the damper.